This invention relates to assaying the level of carcinoembryonic antigen (CEA) in specimens such as sera or plasma. CEA is recognized as a cancer related antigen and its measurement has been used as a marker in diagnosing cancer.
Methods for measuring the level of CEA in sera or plasma have been described in the prior art [Thomson, et al., Proc. Natl. Acad. Sci. (U.S.) 64 (1969) 161; Hansen, et al., Clin. Res. 19 (1971) 143 and Lo Gerfo, et al., New England J. Med. 285 (1971) 138]. Generally, three different immunoassay approaches for measuring the level of CEA present in a specimen of sera or plasma have been described in the prior art. In one approach the plasma is pretreated with perchloric acid solvent in order to separate CEA from interferring proteineous material in the plasma. This approach employs a long time dialysis procedure (about 24 hours), followed by an immunoassay method utilizing 50% saturated ammonium sulfate or zirconyl phosphate gel.
In the second approach, no pretreatment of plasma or sera is used. Instead the plasma is subjected to a double antibody treatment [Egan, et al., Immunochem. 9 (1972) 289]. This approach suffers the disadvantage of requiring a long time period (two or three days) to complete the assay.
The third appraoch [Hirai, H., Cancer Res., 37 (1977) 2267] involves a procedure which uses a paper disc solid phase radioimmunoassay technique. This approach makes use of the so-called sandwich immunoassay technique [solid support-antibody-antigen-labeled antibody: Catt, K. and Tregar, G., Science, 158 (1967) 1570]. In this technique serum or plasma is heat-treated for ten minutes at 85 degrees centigrade in an acetate buffer at pH 5.0. Thereafter, the supernatant is separated and then incubated for approximately five hours with a paper disc to which antibody against CEA (anti-CEA) has been covalently attached. Subsequently, .sup.125 I labeled anti-CEA is added and incubated for approximately 20 hours. The results from use of this approach are obtained after approximately 25 hours.
Unexpectedly it has been found that substituting solid supports having CEA antibody adsorbed thereto for paper disc having CEA antibody covalently bound thereto provides a more sensitive immunoassay. The time for the assay using CEA antibody adsorbed solid support is about one fifth that of the procedure using a paper disc.